Kiip, the US startup that incentivizes in-app ads by making them rewards, has signed its most significant international deal to date after landing a partnership with Yahoo Japan, the largest media company in Japan.

The San Francisco-based company arrived in Japan in January of this year with loyalty program Ponta as its launch partner. Now it has arguably picked up the biggest fish in the country’s media pond through its deal with Yahoo Japan — which is jointly owned by operator SoftBank and Yahoo Inc.

Web measurement service Alexa ranks the main Yahoo.co.jp news portal as Japan’s most visited site. Exact figures for its mobile apps have not been made public, but Kiip founder Brian Wong tells TNW that the company has “tens of millions” of users across its Web and mobile services.

Yahoo Japan will use the Kiip platform to boost engagement with users of its main app for iOS and Android. The deal — which represents the first third-party integration into the app — will serve users with Kiip ads and rewards for completing activities within the app, such as sharing a weather forecast, reading news and more.

The system will give users opportunities to win credit for ‘T Points’, a shared virtual currency program that has 46 million members in the country.

Over time, Yahoo Japan plans to roll the platform out across a wider range of services, including games services and apps, news portals, female-focused media, task management services and cooking and lifestyle media. The idea will remain the same, the more that users interact with Yahoo Japan services, the more opportunities they get to earn virtual coins.

Yahoo Japan has a growing presence on mobile — its main Android app has been downloaded more than 5 million times (Apple’s App Store doesn’t disclose any download data) — but its real presence is on the desktop Web.

Wong says he “wouldn’t discount any possibility” of the relationship moving from mobile to Web as the two companies work together, and that would represent a massive visibility boost for Kiip in Japan. As it stands, just working with Yahoo Japan could help land other clients in the country.

“Online-offline conversions are a big deal in Japan,” he says. “Yahoo Japan has traditionally been strongest on the desktop, but we’re helping them leverage their own system to provide a more compelling and serendipitous experience for users to keep them coming back.”

“Our international strategy is more sharpened since we launched the self-service option,” Wong explains. “We’ve found that this lower barrier of entry, coupled with support for 11 languages, allows a lot of companies to participate.”

Wong says Kiip has handled more than a dozen campaigns across multiple countries in Asia, Japan excluded, which is “indicative of the progress that we’re making worldwide as a company.”

Kiip has raised more $15 million in funding to date, including its $11 million Series B round which was closed in July 2012. The company says its network reaches 75 million users worldwide each month via 1,100 Kiip-enabled apps.